1. Field of the Invention
The present invention relates to a method for forming a variable capacitor, and more specifically a variable capacitor such as that described in French patent application No. 0350911 of the applicant.
2. Discussion of the Related Art
The variable capacitor described in the above-mentioned patent application comprises a conductive layer covering the inside of a cavity formed at the surface of a substrate and a flexible conductive membrane placed above the cavity. According to an aspect of this variable capacitor, the cavity portion covered by the conductive layer has the shape of a groove such that its depth increases continuously from one of the groove edges to the groove bottom. Further, the conductive layer covers the inside of this groove portion at least up to one of its two edges that it may cover.
As described in the above-mentioned patent application, the method for forming such a variable capacitor comprises the forming in a substrate of a partly groove-shaped cavity, of covering the inside of the groove with a first conductive layer, of filling the cavity with a sacrificial portion, of forming on the sacrificial portion a bridge-shaped conductive strip bearing on the lateral groove edges, and finally of eliminating the sacrificial portion. The conductive strip forms a flexible conductive membrane that can deform to come closer or draw away from the conductive layer covering the inside of the cavity.
The forming in a substrate of an at least partly groove-shaped cavity may be performed in various ways such as described in the above-mentioned French patent application. Except for the method for forming a cavity by means of insulating spacers, the other described cavity-forming methods are relatively complex to implement and require a large number of operations. Further, each of these methods provides a cavity having, in cross-section, a groove shape with a well-determined profile without for it to be possible to obtain an “ideal” profile. Further, the shapes of the cavities obtained according to such methods are not homogeneous and depend, among others, on the density of cavities formed on the substrate.